Venous Ultrasound - HD

Introduction

Hello, I'm Larry Needleman.
I'm from the Sydney Kimmel Medical College at Thomas Jefferson University.
I'm one of the radiologists in the division of ultrasound and today we're gonna talk about an update on venous ultrasound.

Deep Venous Anatomy

Let's begin by discussing some deep venous anatomy.
There are two main systems of the venous system, the deep system, and the superficial system.
The deep system lies underneath the muscular fascia and is responsible for returning most of the blood to the heart.
The deep system is divided into the larger central veins and the deep veins of the calf.
The central deep veins are the common femoral vein, femoral vein, deep femoral vein and popliteal vein.
Recently recommendations are that the superficial femoral vein name gets dropped to the femoral vein because some clinicians were misinterpreting the superficial femoral vein as a superficial vein, it is a deep vein for anatomy purposes.
This deep femoral vein and femoral vein join to form the common femoral vein in the upper thigh.
The popliteal vein becomes the femoral vein in the distal thigh.
The calf veins are veins that either lie between the muscles, the posterior tibial peroneal, and anterior tibial veins or the veins that lie inside of the muscles.
Typically, we talk about the gastrocnemius and the soleal veins in their respective arteries.

Superficial Venous System and Connections

The superficial system lies superficial to the fascia and is the great saphenous vein and the small saphenous vein.
There are also tributary veins.
Communicating veins connect one part of a system to another and perforating veins connect the deep and superficial system.
They perforate the fascia and so-called perforating veins.
The other major connections between the superficial and deep system are the great saphenous vein at the femoral vein and the common femoral vein and the small saphenous vein typically at the popliteal vein.

Importance of Venous Ultrasound

The reason this test is important is because DVT is an important disease, it affects hundreds of thousands of Americans each year and is responsible for chronic venous insufficiency and death.
In some patients who develop the most feared complication, pulmonary embolism.

Risk Factors for DVT

The risk factors have been known for quite a while.
Virchow described three risk factors, stasis, vessel wall injury and hypercoagulability.
And the balance between the three are necessary to maintain normal thrombosis in healthy vessels.
For instance, when you are cut.
But when this gets out of whack, thrombosis can occur in healthy vessels and that is what we know as DVT.

Venous Thromboembolic Disease

The entire spectrum of DVT to pulmonary embolism is called venous thromboembolic disease or VTED.
Thrombus tends to begin behind valves and in vessels that have stasis within them.
For the typical patient who has a thrombus after immobilization, the thrombus grows and grows into the lumen and becomes free floating.
It's attached to the wall and can actually fill the lumen and attach to a greater extent in the wall and may have a component of being completely occlusive or just be free floating in the vein.
As the vessel and blood responds to the thrombus, there is thrombolysis occurring on the thrombus.
So there is constantly thrombogenesis and thrombolysis and the balance of the two define how DVT changes over time.
Material that is eaten away at the edges form retraction while the thrombus that is eaten away from the middle causes recanalization and in several months most patients have no residua of the DVT, but in about a third there's scarring and complete occlusion is also possible in some percentage.

Patient Risk Stratification

The medical literature is very concerned about overuse of venous ultrasound and so they divide patients into higher and lower risks.
That is done by a bunch of prediction rules, the most common of which is the Wells prediction rule.
This leads to a score.
You get one point for each of the risk factors and minus two points if you have an alternative diagnosis at least as likely as DVT.
So you can have as low as minus two and as high as eight.
Now the risk factors are typically defined as low risk if you have zero or less points intermediate if you have one to two points or high risk if you have more than three points.
Some iterations of the Wells score just has high and low probability.
But it turns out that these techniques are a good way of evaluating those patients who are at higher and lower risk for deep venous thrombosis.
Those with a low pretest probability, which is about half of your patients, have about an 8% prevalence of DVT in this study and that number is close to other studies as well.
Now a low number of 8% is not low enough to stop or not treat the patient and so something else must be done.
If we go to the high pretest probability, that's about a fifth of our patients, about two thirds of them will have DVT and this is not high enough number to make anticoagulation for all of them.
So imaging is necessary in this group and in the intermediate group as you'd expect, not high or low enough to do anything and therefore further evaluation is warranted.
Therefore, for the intermediate and high risk patient ultrasound is recommended and for the low risk patient, a D-dimer blood test is recommended.
The D-dimer blood test is very sensitive for DVT in most patients, but it's got a relatively low specificity, so there may be false positives if you have a positive D-dimer, the next step is to get an ultrasound so those patients with a low pretest probability and a negative D-dimer can stop.
This has been described in many different pathways.
This is from the American Academy of Family Physicians and the American College of Physicians, and this strategy is a reasonable one.

Reasonable Strategies for Evaluation

So what do we mean by a reasonable strategy?
The risk of DVT after normal venogram, which is the gold standard, is about one to 1.5% in six months.
And so safe strategies can meet this goal.
So what, how can we meet this goal?
One way is with the low pretest probability and a negative D-dimer, which has a three month incidence of DVT of less than 1%.
A low pretest probability and a negative ultrasound is also a safe strategy and a negative whole leg ultrasound study, as we'll talk about a little bit later, is also a safe strategy.

Lower Extremity Duplex Study

The lower extremity duplex study is duplex and therefore has in it color spectral and gray scale ultrasound.
The most important part is gray scale ultrasound, but let's first discuss some of the findings in Doppler.

Doppler Findings

The normal venous system in the deep system has variation in it, which is related to changes in respiration.
And so as we look at the peak velocity of the waveform, it will vary with respiration.
When you have an obstruction to the system, that variation is lost and so the signal is continuous and this may be due to a DVT, it may be due to compression on the vein, either at the level of the signal or above the level of the signal, or it could be scarring from prior DVT with collateralization.
Of course, if you have a thrombosed vessel, the Doppler signal will be absent.
So here we can see a normal spectral Doppler where we can see the nice undulation of the vessel related to respiration.
The abnormal spectral Doppler signal is continuous with little change on this side.
We also use bilateral symmetry to help us and so if there are cases of subtle loss of variation that will be seen by comparing one side to the other in all cases of the lower extremity, at a minimum we compare either the common femoral vein or iliac vein from side to side.
The obstruction that is present is above the level of this.
So if this is the femoral vein, the obstruction could be at the level of the femoral vein above this, the common femoral vein, the iliac vein, or the IVC.
And depending on which vessels are affected, you may figure out which is the site of the obstruction.
So for instance, if the iliac vein is normal, then the obstruction has to be at the common femoral or superficial femoral vein level just above the skin.
If both sides are abnormal, you would expect either bilateral iliac or IVC obstruction.
Now the respiration changes can cross the baseline, particularly in the common femoral vein, but when we see this all the way down the leg, we're worried about vessels which are too pulsatile and showing too much reverse flow typically from cardiac disease or tricuspid regurgitation or elevated right heart strain.

Compression Technique

Compression is a relatively straightforward study.
It's typically performed in the short axis of the vessel and you press on the transducer lightly until the vessel goes away completely.
If there's any question of whether or not you pushed hard enough, if you see distortion of the artery, you've certainly pressed hard enough to make a normal vein go away, that is not usually necessary.
A non-compressible vein is a vein that is filled with something either acute venous thrombosis or scar or you just haven't pressed hard enough.
And so typically we look at the same vessel without and with compression as in this picture side by side images, cine loops or two pictures in a PACS system back to back are all ways to look at the two vessels together.
The long axis view can be helpful to look at the extent of vein and also can help you see some other parts of the anatomy.
So it can be helpful when there is a filling defect.
In the vein here we have a vein which has echogenic material in it.
It started in the great saphenous vein and migrated into the common femoral vein and the edges of it are free floating and it is moving in real time.
So a free floating clot is always acute.
Other signs of an acute venous thrombosis is of a soft filling defect and one that is soft enough to deform while compression with the probe is made.
Veins are also frequently larger from the venous thrombosis and the filling defect is smooth here in a long axis picture of acute DVT, we can see the dilatation of the vein over the center of the picture, whereas at the right side of the picture you can see the normal caliber of the vein is being much smaller.
Gray scale is very helpful and color can be done to show that the filling defect is seen as a filling defect in color.

Thrombus Evolution and Chronic Changes

As the thrombus heals, there may be residual material present and the term for this is still quite variable in the literature.
In the internal medicine literature, the term residual venous thrombosis is used scarring and chronic venous change is also terms that you'll see.
I don't prefer the term chronic DVT because frankly after several weeks this material is fibrotic and no longer a thrombus.
So residual venous thrombosis is an acceptable term.
However, when we look at the material that's left over, we can see that it looks like a fibrotic material which is stiff and it is hard during compression.
It may be irregular.
It's typically incorporated into the vein wall, sometimes over long lengths.
If the recanalization is long, you may just see wall thickening and if the retraction and recanalization occur, you may be left with just material lying inside the lumen of the vein, which can look like a thin wisp like a web or a band of material in the vein, the vein typically is described as normal or small when there's scarring.
Here are some examples of residual venous thrombosis.
We can see irregular material in the vein that's got a long attachment to the vein wall.
Some bright echoes inside of it are probably early calcifications that are forming.
In the next right upper picture we can see the vein has a defect within it and we can see a synechia.
It is somewhat triangular and irregular in shape and if we look carefully we can see some linear lines in the vein indicating the synechia.
On the lower left we can also see the synechia.
It's a little bit area of a little bit thinner, a little bit thicker, and then we have even more thick area.
This was immobile in real time.
And another clue to the fact that this is a scar is that we look at the left side of the vein.
We can see that it's retracted in again, indicating scarring is present.
In the right lower picture, we can see that the residual lumen is in blue and there's thickening of the vein wall from retraction.
Collaterals may be present and they indicate that there is a response to obstruction.
These can occur in scarring, but since scarring may also be associated with new DVT, the presence of collateral does not exclude acute venous thrombosis.
Collateralization can occur in several different ways as collateral vessels that grow around the area of obstruction or dilatation of the venules in the vein wall itself, this case has both examples.
In the right side of the image, the lower squiggly line is on the vessel wall being venule, whereas the upper color going into the lumen is a collateral vessel.
Depending on who you read, you may get different interpretations of what is an adequate exam and in terms of what is considered an adequate exam, the study from the inguinal ligament to the knee is a minimum amount of imaging that is recommended from both the AIUM, the ACR and the Intersocietal Accreditation Commission in vascular testing.
The accreditation commission also recommends that the calf is imaged for the AIUM and ACR calf vein imaging is selective.
If you have a study that is normal but the patient has calf symptoms, it is recommended that you look over the area of symptoms to make sure that there is not calf DVT to explain the symptoms that are present.
If one only looks above the knee, patients may get a negative study even though they have symptoms below the knee.
If you do studies just to the knee, then you need to be somewhat liberal in ordering follow-up studies since calf DVT may be missed.
The imaging documentation guidelines are a little bit different from study to study for the AIUM a picture without and with compression of the common femoral saphenofemoral junction, proximal deep femoral vein proximal and distal femoral vein are recommended as well as a picture of the popliteal vein for the IAC.
You can see some other pictures are recommended.

Patterns of Deep Venous Thrombosis

When one sees patients with deep venous thrombosis, it is striking that you can see areas of venous thrombosis separated by areas of normal vein and then other areas of venous thrombosis.
And that's because venous thrombosis grows in response to local changes in the vein wall as opposed to growing like a weed from one spot to another and independent thrombi develop in the lower limbs.
Although the calf veins are thought to be the origins of most of the vessels and in fact this is worked out by looking at phlebography where calf DVT is present in 83% of patients having venograms who are symptomatic isolated calf DVT is present in about a third of patients so the calf can be examined.

Calf Vein Imaging

Typically we look at the posterior tibial and peroneal veins from the ankle to the knee.
Some technologists scan from the ankle to the knee to see it at the ankle easier and then scan in the knee where it can be more difficult depending on the size of the knee and the size of the muscle.
We also look at areas of symptomatic pain and we try to get some pictures that can resolve some of the pictures of the gastrocnemius and so vessels that also lie within the plane of the image when you're looking for the posterior tibial and peroneal vein.

Controversies in Calf DVT Imaging

Now why is calf vein imaging so controversial?
Some people feel that calf DVT rarely causes pulmonary embolism and the decision to treat or not treat calf DVT is currently controversial so those who feel that it's not important to treat don't feel that imaging is important.
In most patients, calf DVT is self-limited and will go away in at least 80% of patients.
And so it's a transient process which will never propagate to more central disease.
However, 20% of patients may get femoral popliteal disease after calf DVT and we need to figure out a way if we don't treat on how to identify those patients.
So we do that by recommending a followup ultrasound at one week.
For thigh, the need to ultrasound negative DVT and those with calf DVT, the patients who you don't look at the calf may have high risk and shouldn't be ignored, particularly if there are continuing symptoms.
Calf DVT looks like any other form of DVT.
In this case we can see that there is several groups of veins in the calf.
The posterior tibial, the peroneal, the peroneal typically lie right near the fibula.
They also have the name of the fibular vein and you can see that there is a vein that lies within the muscle here in the midcalf representing the soleal vein with compression.
The posterior tibial is compressible, the peroneal is compressible, but the soleal vein stays non compressed and therefore it is an acute calf DVT in the muscular calf vein.

Consequences of Calf DVT

Now for those of us who feel that DVT should be evaluated, it's because there are important consequences to calf DVT.
While scanning the vein, I mentioned before that 20% will develop femoral popliteal DVT, but chronic venous insufficiency can occur after calf DVT.
Calf DVT may put patients at slightly higher risk for a new episode of DVT.
Some patients with calf DVT may also develop malignancy after the study is performed and the mortality if you have bilateral calf DVT is higher than patients without DVT.
We wanna remember that the calf veins in the muscle are in fact deep venous thrombosis.
You may see veins in the superficial system and that's superficial thrombophlebitis.
But again, those are not the deep veins and it's important not to confuse the deep calf veins with superficial veins.

Recurrent DVT

Recurrent DVT can occur up to a quarter and that's a new episode of acute DVT after a prior DVT.
This may occur at the site of scarring or it may occur in an entirely new place.
It can be a very difficult diagnosis, particularly if you don't have a baseline at the end of treatment when patients return with symptoms.
So the best line is a new DVT away from a site of prior DVT or enlargement of the clot compared with an earlier scan.
But anytime you see acute appearing DVT on either on an area of scar or in an area of vein, you need to worry about recurrent DVT.
Now dilatation may not be easy to do in a vein that is scarred because the vein may not allow itself to be dilated because it's scarred down.
So dilatation is not a good sign, but soft material deformable material and free-floating material can be helpful.
Some people have looked at the size of the vein and looking at changes in the size of the vein to be helpful.
In this group of images we can see a popliteal clot which was initially eight millimeters, which at seven months scarred down to four millimeters but did not go away by the way.
This puts the patient at continuing risk that's higher than patients who have complete clearance of their veins.
A few months later the patient returns with symptoms but the vein did not change size so there's no acute DVT a few months after that.
However, the patient returns and that material did increase in size to nine millimeters.
So this is now acute DVT on top of a scar and then months after that we can see that it's scarred back down to four millimeters.
Here we can see that there's a bullae in the vein you can see the bright echogenic material with shadows and there's some mid-level echogenicity on the vein and when you press, you can see that material is change shape and deform indicating acute deep venous thrombosis on bullae or acute DVT on scar, also known as recurrent DVT.
And this patient should be treated with anticoagulation.

Deciding When to Stop Anticoagulation

Some people look at ultrasound and other techniques to help decide when anticoagulation could be stopped.
If the recurrence risk is still high, the rationale goes then keep the anticoagulate longer.
So some people use the length of treatment and the length of risk factors and some people draw a D-dimer if it remains elevated.
The patient is a continuing risk for a new recurrent DVT, but some people also use ultrasound to look at residual venous thrombosis and see if there's residual material because anything over a few millimeters puts the patient at higher risk and anticoagulation may or may not be stopped based on the risk of continuing it.
Obviously since there are important risks of giving a anticoagulant.

Follow-up Studies

So one does a negative venous ultrasound, is that good enough?
We know that in the standard patient with a new onset of deep venous thrombosis without a history, a study that goes from the calf to the ankle is a safe strategy.
However, other patients you don't know if this is safe strategy, what does that mean?
If the patient had a prior DVT, we don't know if one study is safe.
If a patient is pregnant, we don't know if one study is safe.
So we are rather liberal in recommending a follow up in one week and we say that in our report by saying if there is continuing or high concern for acute DVT consider follow up in five to seven days.
Who do we typically add this to?
Patients who have negative DVT with inadequate or no calf patients with a negative study with prior history of DVT patients with a negative study during pregnancy, patient with a negative study who had quality issues and some of us added also from the emergency room since we don't know if they are at high, medium or low risk.
And in patients with a negative DVT study with scarring in the vein, we also don't know what happens to the patients frequently when a calf DVT is diagnosed.
And so in those groups we need to recognize that if they're not anticoagulated then a follow up is necessary.
And so we report this as a follow up in five to seven days is recommended to exclude progression if the patient is not treated.
If there's no change in one week, we repeat the study and if there's still no change then we repeat it one more time.
But if there is a new DVT or extension of calf DVT that's we consider significant, we will treat at that point.

Echogenicity of Thrombus

There are some gray scale issues that are somewhat problematic based on what some people have reported.
The echogenicity of thrombus changes during treatment.
Other people have not found this to be so.
In my experience, the echogenicity of clots, particularly with modern machines, is not predictive of how long the clot has been there.
And Dr. Murphy and Cronin have described this many years ago where they looked at the echogenicity of thrombus based on the age of symptoms and you can see that there's no relationship between echogenicity and thrombus.
You may have heard that fresh clot has poorly echoic and new clot has echoes inside of it, but it's not necessarily true.
Here we have a patient with an acute DVT.
You can see that it's got some mid-level echoes within it and here we can see the same thrombus at the first scan on the left having mid-level echoes and the scan on the right which is virtually anechoic except for some echogenic material at the edge.

Unilateral vs. Bilateral Studies

Another question that frequently comes up is, should the study be done unilaterally or bilaterally?
And this has been looked at by a variety of authors and in this particular paper they looked at the risk of DVT on the asymptomatic side when the symptomatic side is normal.
So you do the symptomatic side, do not find the DVT.
What are your chances of finding a clot on the other side?
For all patients it's about 1%, but there are some subsets where there is a higher amount.
If you have malignancy, the chance can be as high as 4%.
If you've had recent joint surgery, 5% if you have a hypercoagulable state, 9% and if you had a past DVT about 2% inpatients also have 2%.
So in these groups we do recommend looking at a bilateral study in all patients.
For other outpatients we just do a simple unilateral study recognizing that all patients get that common femoral or iliac spectral Doppler on both sides.

Non-DVT Findings

We can also recognize that many patients don't have DVT.
So what do they have?
They could have chronic venous insufficiency, they can have heart failure and musculoskeletal or other soft tissue abnormalities.
They can have arterial disease and others.
So let's look a few of these before we can complete the lecture.
Here we can see that there's echogenicity in the subcutaneous space related to edema.
You can see that the fibrous septa inside them look dark because although they look bright in normal patient, all echogenicity is relative.
So the echogenic subcutaneous edema makes it look dark.
Here it looks a little bit more fluffy, but also a case of edema.
We can frequently see Baker cysts that rupture that are related to patient's pain.
Typically when they present with popliteal pain, the popliteal cyst or Baker cyst is seen and it can be ruptured or be an indicator that there is an arthritic condition in the leg.
And the specific popliteal cyst called the Baker cyst is identified when it's seen to protrude between the semimembranosus tendon and the proximal gastrocnemius.
Muscle fluid collections can often cause pain, particularly if there's been trauma or infection.
They may look similar and they may need aspiration or diagnostic history to figure out what the particular diagnosis is.
In particular, hematomas can be quite variable in echogenicity from virtually anechoic all the way to echogenic based on how the age and the breakdown of the blood occurs.
Lymphoceles are generally anechoic as are seromas and abscesses can be quite variable, but low level echogenicity and heterogeneous material is typical.
They may or may not have hyperemic walls by color Doppler.
Here's a patient who presents in the lateral calf in a patient with trauma.
That was no DVT, but this subcutaneous hematoma was identified in this patient.
The site of pain was at the knee joint and we can see that there is fluid from the knee protruding and echogenic material in the wall of this material indicating pannus.
This patient does not have trauma, but this muscle is quite abnormal with varying echogenicity and you can see a bright area in the center of the left image.
This is actually a patient who has necrotizing fasciitis or necrotizing soft tissue infection.
This could also be myonecrosis if the patient's diabetic.
And so when you see musculoskeletal abnormalities, it's important to recognize where they're coming from.
If you can render a specific diagnosis, do so.
And if not, please send the patient to the appropriate imaging test where they can get the appropriate diagnosis.

Summary

So in summary, the gray scale differentiation of acute thrombus from scarring can differentiate acute from chronic and over 95% of patients in the acute venous thrombosis we're looking for non-compressible and deformable veins with a smooth margin.
They may be free floating, although this is less frequent and the vein is frequently enlarged.
The scarring or residual venous thrombosis has a non-compressible, non deformable material in the vein in a irregular margin and it's incorporated into the vein wall.
The vein size is either normal or small.
You may see circumferential wall thickening, irregularities of the lumen or webs echogenicity in the presence of collaterals are not particularly helpful.
I hope this lecture was of help to you. Thank you.